Potassium Is a Very Reactive Metal

Potassium is a very reactive metal. Many of its compounds are not very reactive. For example, some class B fire extinguishers contain potassium bicarbonate as a dry powder for use in extinguishing burning liquids. Why is there such a difference in the reactivity of potassium in the bicarbonate salt and potassium that is a combustible metal?

A) The difference in reactivity really is not that great to warrant an explanation.
B) The potassium atom is bonded to an oxygen atom in the bicarbonate salt but is unbonded in the metal and free to react.
C) The potassium metal possesses one additional electron that is easily transferred to other substances; the potassium in the bicarbonate salt already has lost this reactive electron.
D) The potassium in the bicarbonate salt is a base, but the potassium metal is an acid.
E) The potassium in the bicarbonate salt is an acid, but the potassium metal is a base.